Coal is the world's most plentiful fuel and the United States has an abundant supply. Currently, 86% of coal consumption of the United States goes to generating electricity and about 55% of electricity generated is produced from coal. Most of the coal presently being consumed is by direct combustion of finely pulverized coal in large-scale utility furnaces for the generation of electric power. In the last two decades, an integrated Coal Gasification Combined Cycle (IGCC) has been developed to produce electric power. IGCC consists of coal gasification, Brayton cycle and Rankine cycle. A gas turbine is operated in a Brayton cycle mode while a steam turbine works in a Rankine cycle. Exhaust of the gas turbine is used to generate steam for the steam turbine. Energy efficiency of IGCC is in a range of 40-47%.
Coal fired power industries, along with other fossil fired power plants, generate significant pollutant emissions including nitrogen oxides (NO.sub.x) sulfur oxides (SO.sub.x) and carbon dioxide (CO.sub.2). Sulfur oxides and nitrogen oxides can be controlled to some extent by emission devices at considerable cost. However, removal of power plant CO.sub.2 emission requires significant amounts of energy leading to a 30-40% reduction of energy efficiency. However, the removal and sequestering of power plant CO.sub.2 emission is a definite goal of international community, as CO.sub.2 is a major contributor to global warming effect.
The present invention broadly embodies an S Cycle Electric Power System (SCEPS) with high energy efficiency and zero pollutant emissions including CO.sub.2. In SCEPS coal is gasified, and burned in the S cycle. Sulfur and other pollutants are removed before combustion. Combustion gases basically consist of CO.sub.2 and water vapor, and are used to generate power in three free turbines. Most of the exhaust of the third turbine is used to heat the recycled CO.sub.2 and O.sub.2, and to generate steam for coal gasification. The rest of the exhaust is utilized to produce steam for a steam turbine system. The energy efficiency of SCEPS is higher than the IGCC, e.g. 49-51%. When a CO.sub.2 removal unit is not included in SCEPS, the energy efficiency increases significantly, e.g. 59-61%, leading to a reduction of CO.sub.2 emission in terms of kg CO.sub.2 /kWh. SCEPS can also burn natural gas instead of the synthetic gas produced from coal gasification.